This invention relates to polymer blends comprising at least one tapered conjugated diene/monovinylarene block copolymer and at least one styrenic polymer.
Copolymers of conjugated diene/monovinylarene are known and useful for a variety of purposes. Of particular interest are polymers that can be formed into colorless, transparent articles having good physical properties, such as impact resistance. Such articles are useful in toys, window pieces, beverage containers, and packaging such as blister packaging.
The polymers should also exhibit sufficient thermal stability to be suitable for use with conventional injection molding equipment. For many applications copolymer blends containing high amounts of styrene are required. Such polymers are generally prepared by blending certain monovinylarene-conjugated diene copolymers with styrene polymers. However such blends often contain an undesirable haze and blue coloration. It would therefore be desirable to develop polymers and polymer blends having a combination of low blueness, good clarity, hardness, stiffness, and toughness.
It is an object of this invention to provide a polymer useful for preparing blends having good optical clarity.
It is another object of this invention to provide a process for preparing such polymers having good optical and mechanical properties.
In accordance with this invention a block copolymer comprising at least three consecutive conjugated diene/monovinylarene tapered blocks is provided. As used herein, consecutive means three sequential tapered blocks with no intervening homopolymer blocks. The tapered blocks contain a mixture of monovinylarene and conjugated diene.
In accordance with another aspect of this invention, a polymer blend comprises at least one coupled conjugated diene/monovinylarene block copolymer and at least one styrenic polymer, wherein the coupled conjugated diene/monovinylarene block copolymer is produced by a process comprising sequentially contacting under polymerization conditions at least one monovinylarene monomer, an organoalkali metal initiator, at least one conjugated diene monomer, and thereafter coupling with a polyfunctional coupling agent to form the block copolymer; at least three consecutive monomer mixture charges containing monovinylarene monomer and conjugated diene monomer are provided to produce at least three consecutive conjugated diene/monovinylarene tapered blocks in the block copolymer; all the monovinylarene monomer and conjugated diene monomer contained in each charge are added at the beginning of the charge allowing excess of monomer to be present in the reactor; the at least one monovinylarene monomer contains from 8 to 18 carbon atoms, and the at least one conjugated diene monomer contains from 4 to 12 carbon atoms, and the styrenic polymer is selected from the group consisting of at least one copolymer produced by copolymerizing at least one styrenic co-monomer and at least one unsaturated oxygen or nitrogen containing co-monomer.
In yet another aspect of the present invention, the styrenic polymer (excluding styrene homopolymers) is selected from the group consisting of at least one copolymer produced by copolymerizing at least one styrenic co-monomer and at least one unsaturated oxygen or nitrogen containing co-monomer; wherein the polymer blend comprises 60 wt % or more of the coupled conjugated diene/monovinylarene block copolymer; the monovinylarene monomer is selected from the group consisting of styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-ethylstyrene, 4-t-butylstyrene, xcex1-methylstyrene, and mixtures thereof; the conjugated diene monomer is selected from butadiene, isoprene, 2,3-dimethylbutadiene; the styrenic co-monomer is selected from the group consisting of styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-ethylstyrene, 4-t-butylstyrene, xcex1-methylstyrene, and mixtures thereof; and the unsaturated oxygen or nitrogen containing co-monomer is selected from the group consisting of methyl acrylate, ethyl methacrylate, methyl methacrylate, ethyl methacrylate, glycidyl acrylate, glycidyl methacrylate, acrylonitrile, and mixtures thereof.